On Mon, Jun 02, 2014 at 03:06:13PM +0200, Lukáš Czerner wrote:

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So what will happen when there is not enough space when "inserting a
range" ? And how should user proceed from there ?

If insert range fails with an ENOSPC error, user could use collapse
range on the same range to remove the hole.
And after freeing more space, he can again try inserting range.
Ofcourse, this type of guidance should be properly documented in
manpage. When updating fallocate(2) manpage, I will keep  in mind to
describe ENOSPC handling.

Why collapse ? The hole is already there right ? Why not just use
fallocate to allocate the space for the hole. And that's my point
actually. Why not do it this way in the first place, because this is
really counterintuitive.

It's worse than that.  It's possible that the reason why you got the
ENOSPC warning was because the operation to move the extents down
required allocating a block, and it was *that* block allocation which
failed.  So it's not deterministic whether or not the file's extent
mappings were modified after a ENOSPC error, and so it's not clear
whether or not a collapse_range function will undo the range that had
been inserted --- or whether it ends up deleting existing data blocks.

In generally, you really want system calls to have all-or-nothing
effects, where if the system call returns an error, the state of the
file has not been changed.  And for that reason, I agree with Lukáš
that it is really a good idea to decouple moving the blocks down, and
allocating space --- and to make sure that if there is any failure
while inserting the range, the state of the file is not modified at all.

Okay, I will remove allocating space part in insert range patch.
But renaming flags as FALLOC_FL_INSERT_HOLE is needed to concent with
XFS people. Because Dave prefered to call it FALLOC_FL_INSERT_RANGE
so that it looks like it is related to collapse range.

Hi Dave.
Do you have any objection about renaming as insert hole ?

Thanks for opinions!

Cheers,

					- Ted

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